Process for removal of carbon dioxide from mixtures containing carbon dioxide and methane

Abstract

An absorptive distillation using a C 7 to C 8 physical solvent without overhead condenser-reflux duty is described for separation of carbon dioxide from methane, wherein the separation preferentially uses heat energy in contrast to mechanical energy or power.

What is claimed: 
     
       1. A process for the physical solvent absorptive distillation of a feed gas stream containing carbon dioxide, methane and heavier hydrocarbons to produce a methane-rich overhead product and a CO 2  -rich bottom product comprising the steps of: (a) introducing a feed gas stream comprising carbon dioxide, methane and heavier hydrocarbons into an absorptive distillation zone at elevated pressure;   (b) introducing a physical solvent in the amount of approximately 0.5-5 moles of solvent per mole of feed into the upper zone of the distillation zone to absorb CO 2  and heavier hydrocarbons from such feed gas stream;   (c) withdrawing a methane-rich overhead stream from said distillation zone as a product without subjecting it to any overhead condenser-reflux duty;   (d) removing heat from said distillation zone in at least one intermediate stage of the distillation zone between the point of entry of the physical solvent and the feed location;   (e) removing and heating the CO 2  and heavier hydrocarbon-containing physical solvent at approximately the elevated pressure of the feed gas stream to separately recover at least a regenerated physical solvent for recycle to step (b) and a CO 2  -rich bottom product.   
     
     
       2. The process of claim 1 wherein the feed gas stream is at a pressure in the range of approximately 200 to 1000 psia. 
     
     
       3. The process of claim 1 wherein the feed gas stream is initially cooled to a temperature in the range of approximately 0° F. to 50° F. 
     
     
       4. The process of claim 1 wherein heat is removed from said distillation zone in two intermediate stages. 
     
     
       5. The process of claim 1 wherein the intermediate stage is approximately midway between the point of introduction of the physical solvent and the point of introduction of the feed gas stream. 
     
     
       6. The process of claim 1 wherein the heat removal of step (d) is accomplished by removal of distillation zone fluid, cooling of said removed fluid by heat exchange with a source of refrigeration and return of the cooled fluid to said distillation zone. 
     
     
       7. The process of claim 1 wherein the heat of step (e) is provided in the range of approximately 50° F. to 150° F. 
     
     
       8. The process of claim 1 wherein the separate recovery of physical solvent and CO 2  -rich bottom product is accomplished by distillation at relatively high pressure. 
     
     
       9. The process of claim 8 wherein the pressure is in the range of approximately 300 to 400 psia. 
     
     
       10. The process of claim 1 wherein the physical solvent of step (b) is precooled to a temperature of approximately 0° F. to 50° F. before being introduced into the distillation zone. 
     
     
       11. The process of claim 1 wherein hydrocarbons in the range of C 2  to C 5  are separately recovered from the CO 2  and heavier hydrocarbon absorbed physical solvent in step (e). 
     
     
       12. The process of claim 1 wherein the physical solvent is selected from the group comprising C 7  to C 8  hydrocarbons and mixtures thereof. 
     
     
       13. The process of claim 1 wherein the feed gas stream is essentially in the gaseous phase. 
     
     
       14. The process of claim 1 wherein in step (e) a methane-rich stream is separately recovered and recycled to the feed gas stream. 
     
     
       15. A process for the physical solvent absorptive distillation of a gaseous feed stream containing carbon dioxide, hydrogen sulfide, methane and heavier hydrocarbons to separate an essentially methane overhead product and an essentially CO 2  -rich and H 2  S-containing bottom product comprising the steps of: (a) cooling the gaseous feed stream to a temperature in the range of 0° F. to 50° F. at an elevated pressure of 200 to 1000 psia.   (b) introducing said cooled feed stream in the gaseous phase into a physical solvent absorptive distillation zone operated at 0° F. to 50° F. and 200 to 1000 psia;   (c) introducing a physical solvent, in the liquid phase, comprising of C 7  to C 8  hydrocarbons, into the upper zone of the distillation zone at a flow rate and temperature to maintan a constant temperature in said distillation zone and to selectively absorb CO 2 , H 2  S and heavier hydrocarbons from said feed stream.   (d) withdrawing an essentially methane overhead product from said distillation zone without subjecting said product to cooling by condensation or reflux duty from a refrigeration source;   (e) removing the heat of absorption from said distillation zone in two intermediate stages of the distillation zone between the point of introduction of the physical solvent into said zone and the point of introduction of said feed stream into said zone by removing a portion of the distillation zone liquid in each said stage for cooling by heat exchange with a refrigeration source before returning said cooled liquids to said zone;   (f) removing the CO 2 , H 2  S and heavier hydrocarbon-containing physical solvent from said distillation zone and heating it at essentially the feed stream elevated pressure in a second distillation zone to separately recover a regenerated essentially physical solvent, an essentially CO 2  -rich and H 2  S-containing bottom product and a methane-rich stream for recycle to said feed gas stream; and   (g) cooling said regenerated physical solvent to a temperature of approximately 0° F. to 50° F. by heat exchange against a refrigeration source and introducing said cooled solvent into the distillation zone as the solvent of step (c).   
     
     
       16. The process of claim 15 wherein the gaseous feed stream is the product of a CO 2  miscible flood enhanced petroleum recovery process and said CO 2  -rich, H 2  S-containing bottom product is reintroduced into the recovery process to enhance the petroleum recovery. 
     
     
       17. The process of claim 15 wherein hydrocarbons in the range of C 2  to C 5  are separately recovered from the CO 2 , H 2 , and heavier hydrocarbon-containing physical solvent in step (f).